The present invention relates to separation of heavy petroleum hydrocarbons from admixture with inorganic particulate material. More particularly the present invention relates to a process wherein tar sands, or other mixtures of heavy petroleum with sand or similar particulate material, is treated under mild conditions with an aqueous solution of an ammonium salt selected from ammonium sulfite, ammonium bisulfite, and mixtures thereof for separation into bitumen substantially free of sand, and sand substantially free of bitumen.
Tar sands (also known as oil sands and bitumen sands) occur naturally in earth formations ranging in depth from surface deposits to several thousand feet. Such, tar sands are unconsolidated sand deposits impregnated with dense, viscous petroleum. The petroleum is a bitumen (i.e. soluble in carbon disulfide) and has a density at 60.degree. F. slightly greater than water. Up to about 50% of the bitumen may be distilled without cracking and a substantial portion of the bitumen comprises asphaltenes and resins.
Recovery of tar sands from earth formations may be accomplished by surface mining techniques wherein the tar sands are transported to processing units for separation of bitumen from sand. Alternatively, in situ recovery techniques, such as fire floods, emulsion steam drives or solvent drives may be employed for recovering bitumen and leaving sand behind in the earth formation. Bitumen so recovered, even with in situ recovery techniques, may contain substantial amounts of sand in admixture therewith.
Processes are known for recovering bitumen substantially free of admixed sand. Such process include extraction with anhydrous solvent; bitumen separation employing a water-hydrocarbon mixture at about 70.degree.-200.degree. F. and a water pH of 9-9.5; bitumen separation employing water at about 70.degree.-200.degree. F. and a pH of 8-8.5.
The anhydrous solvent recovery processes require large amounts of expensive solvents which must be recovered by distillation for recycle. Thus, such processes are expensive to operate, and require substantial energy input.
The various techniques for recovering bitumen employing water or water-hydrocarbon mixtures are all operated in the basic pH range. In the presence of polyvalent ions, clay minerals tend to flocculate with the bitumen under basic pH conditions, forming slimes which are difficult to separate from the water. Additionally, the bitumen tends to form a froth, or emulsion which must be further treated to recover bitumen free of water.